The present invention relates to a method and a system for evaluating qualities of articles such as electric/electronic apparatuses for home use, products for office-automation (OA) and the like which are manufactured by assembling constituent parts. More particularly, the present invention is concerned with a fraction defective estimating method for estimating likelihood of occurrence of failure in the works involved in assembling an article, a system for carrying out the fraction defective estimating method and a storage medium storing therein data, information and program for executing the method.
Methods known heretofore for determining the fraction defective are primarily so designed as to estimate the causes for occurrence of defects, failures or the like, starting from the defect events or failure phenomena which have actually taken place. As the hitherto known typical methods of estimating the cause of failure or detect on the basis of the contents of the failure phenomenon or the defect event actually or really taken place at a stage in the course of manufacturing process, there may mentioned those disclosed in Japanese Unexamined Patent Application Publication No. 167631/1989 and Japanese Unexamined Patent Application Publication No. 196900/1994. These methods are based on such techniques that real records of defects occurred in the past are stored together with data concerning the causes of such defects in order to allow a degree of correlation between a defect pattern and the cause for the defect to be determined, whereon the cause for the defect is estimated on the basis of the correlation as determined. Further, as the diagnosis techniques in which the similar techniques are adopted, there may be mentioned those disclosed in Japanese Unexamined Patent Application Publication No. 13617/1995 and Japanese Unexamined Patent Application Publication No. 271587/1995.
However, any one of the known methods mentioned above is directed to the technique for estimating directly the causes of defect events or failure phenomena on the basis of the contents of such defects or failures which have really taken place for the purpose of allowing correcting or repairing work to be carried out speedily and properly.
On the other hand, as a method or procedure for performing in advance a quality evaluation of an article to be manufactured before failure or defect really occurs, there is known an FMEA (Failure Mode and Effects Analysis) technique which can already be adopted in the stage of designing the article to be manufactured. According to this method, an evaluator himself or herself predicts "failure phenomena which may occur in relation to individual parts constituting an article" and summarizes the "failure phenomena or events together with relations to the individual parts in the form of a list. Thus, by referencing the list, the evaluator himself or herself can predict "what sort of influence the article as manufactured will suffer when certain failure(s) or defect(s) occurs". In this way, high-quality design suffering substantially no unintentional omissions can be realized.
Further, there is known a method or procedure for estimating seriousness of defects or failures relating to individual parts, respectively, by determining the probability of occurrence of failure phenomenon in relation to the individual parts as estimated by the evaluator (which probability is termed the fraction defective) and then estimating the degree of seriousness of defect of an article as manufactured which can be considered as being ascribable to the defect(s) of the individual parts. As a typical one of such techniques, there may be mentioned FMECA (Failure Mode, Effects and Criticality Analysis) technique.
However, any one of the conventional methods or techniques mentioned above is not in the position to estimate the potential of detector failure to occur in a given article with high accuracy. This is because substantially all the failure phenomena which may actually occur have to be grasped in the case of the conventional methods.
Under the circumstances, not a few manufacturing failures actually take place due to insufficiency of examination or studying, presenting one of the factors for deterioration of the quality of the manufactured article.